The Senate's passage of the resolution of ratification of the New START treaty should be greeted as good news by sensible people interested in a sound American foreign and defense policy. The administration's willingness to accommodate Republican concerns on missile defense and modernization of the aging nuclear force has significantly strengthened the original modest agreement. In exchange for Republican acceptance of relatively small cuts in nuclear weapons, President Obama is now on record supporting missile defense in a way that he had not been before and has committed more than $80 billion to modernizing the nuclear arsenal. Republicans ought to be delighted with the deal.

And while bipartisanship is not always a virtue, in this case it has positive ramifications in the real world. Other nations need to know, at a moment when there are doubts, that the American political system can pull itself together and make a decision. Note how many of America's allies weighed in before the vote in favor of passage. This was not just about the merits of the treaty. It was an implicit plea for the United States to show some domestic unity as a necessary foundation for world leadership. The idea that Washington could tie itself in partisan knots over such a small matter was disturbing to those who are finding themselves once again in need of a strong and capable United States. Even Obama-hating Republicans need to remember that we have only one president at a time, and it's in our national interest that he be regarded around the world as someone who can speak and act with broad national support. In this case, he earned that support by working hard to address the legitimate concerns of the other party.

The internationalist coalition that passed this treaty will be critical in advancing U.S. interests over the coming years: in dealing with Iran; China; the continuing war in Afghanistan; the stabilization of Iraq; the ratification of free-trade agreements with South Korea, Colombia and Panama; and the maintenance of adequate defense and foreign affairs budgets. With the right presidential leadership, this muscular internationalism ought to, as it has in the past, provide the center of gravity for American foreign policy.

Those concerned about the administration's "reset" policy toward Russia should also be glad about passage. Relations with Moscow are about to grow more challenging. This is partly because some of the easy pickings - including this treaty - have already been harvested. The problems that lie ahead are going to be a tougher test of the reset: what to do about Russia's continued illegal occupation of Georgia; how to handle Russia's increasingly authoritarian domestic behavior, its brutal treatment of internal dissent and its squelching of all democratic institutions. Nor are we likely to see much Russian enthusiasm for a round of tougher sanctions on Iran. Had the treaty been defeated, any failures and setbacks on those issues would have been blamed on Republicans. Passage of New START means that responsibility will fall where it belongs: on Moscow and on the limitations of reset.

Republicans and Democrats who care about these issues should start thinking about how to hold Moscow and the Obama administration accountable. How should the United States provide strategic reassurance to Eastern European allies nervous about Moscow's intentions? How can we help Georgia maintain its independence and begin the process of regaining sovereignty over Russian-occupied territories? What kind of legislation can be useful in putting pressure on the Russian government to ease repression and allow democratic institutions some breathing room?

There are considerations beyond the U.S-Russia relationship as well. Republicans made a big show of their concern about the administration's attitude toward missile defense. Fair enough. But have they demanded more funding for missile defense programs with the same determination that they demanded more funding for nuclear modernization? Republicans are right to claim that at a time when nuclear proliferation seems on the verge of spiraling out of control, missile defenses are more necessary than ever. But this needs to be more than a talking point. Will the next, more Republican Congress put money where its mouth is?

These issues were always more important than the cutting of a few hundred warheads. Many observers believe the fight over New START was just about politics. Now that the fight is behind us, let's hope that the president and his opponents prove otherwise.

Robert Kagan, a senior fellow at the Brookings Institution, writes a monthly column for The Post.